When cells die in vivo and undergo necrosis they invariably stimulate an inflammatory response. This causes considerable collateral damage to adjacent healthy tissue and is thought to underlie the pathogenesis of a number of acute and chronic diseases. A number of other particulate stimuli (urate, silica, asbestos, iron oxide, etc.) also stimulate sterile inflammation that leads to disease. The overall goal of this grant is to elucidate the mechanisms by which dead cells and other sterile particulates stimulate inflammation. In Aim 1 we will define the cellular surveillance mechanisms in vivo that sense cell death and other irritant particulate stimuli and in response trigger an acute inflammatory response. The hypothesis underlying this Aim is that cells of the innate immune system function as sentinels that monitor tissues for these stimuli and upon detecting them produce IL-1 that then drives the acute inflammatory response. The goal of this aim is to test this hypothesis and to define the key cell types involved in this process. We will also test the role of these mechanisms in causing tissue damage and disease. Our second Aim seeks to elucidate the cell biological and molecular pathways through which dead cells and sterile particulates stimulate innate immune cells to produce IL-1. Our underlying hypotheses are that: (i) These particulate stimuli must be internalized into phagosomes of macrophages; (ii) After internalization the key event that leads to macrophage activation is rupture of some phagosomes; (iii) The resulting release of activated phagosomal contents into the cytosol is sensed by the NOD-like receptor NLRP3; and (v) Cathepsins are the key mediators released from phagosomes that activate NLRP3 to induce IL-1 production. The goal of this Aim is to test these hypotheses. The importance of these hypotheses is that they offer a new and testable paradigm, which if correct will reveal a common unifying pathway and identify tractable molecular targets for therapeutic intervention.